In order to construct a comprehensive thesaurus in medical science, our research project for three years has proceeded in the following procedures ;For the first years, we collected the existing thesaurus, terminologies and classifications in medical science, and reviewed their policies and schema. We found that each of them is used by various kinds of users, and has a different system of organizing terms. It means that those users must find different terms from different thesauri, when they need to retrieve various databases relevant to the thesauri. There is a definite necessity to improve this inconvenience for users, by constructing an appropriate system, so that users can use their terms commonly to all the databases.The idea is a meta thesaurus, which can translate all the medical terms into those relevant to each database.For the second year, we analyzed such a meta thesaurus proposed by National Library of Medicine, called UMLS(Unified Medical Language System), and the thesaurus for Igaku Chuo Zasshi(Japana Centra Revuo Medicina). Comparing both of them, we studied the basic schema for a comprehensive meta thesaurus converse to Japanese and English.We also organized a preparatory study of 'information seeking behavior' of future users of this thesaurus.For the third year, we examined the possibility of introducing MeSH terms and MeSH category codes into the thesaurus for Igaku Chuo Zasshi.By this research project, we can now present the main requirements for constructing a comprehensive thesaurus in medical science.The combination of the thesaurus for Igaku Chuo Zasshi and UMLS, based Medical Subject Heading, is now available.